1. Field of the Invention
This invention pertains generally to methods and apparatus employed to remotely view the walls and internal structures of combustion chambers. In particular, the invention relates to methods and apparatus for use in coal, gas, or oil fired furnaces.
2. Description of the Prior Art
A major difficulty exists in examining internal walls and internal structures of combustion chambers while in operation. Intense ambient light and heat from the combustion flames makes it difficult to make out structural and surface details due to the lack of contrast. In addition, the spectral content of the ambient light produced by the combustion flame usually contains certain dominant wavelengths which are largely determined by the type of fuel being used. When external sources of light are used to illuminate these structures and surfaces, it is difficult to discriminate the ambient light from the external source. This further complicates the problem of accurately observing details of the structures and surfaces to be studied.
The presence of intense light and heat is a particular problem when a human observer examines the combustion chamber through a viewing port, for example. Special equipment in the form of protective eye and or body wear in the obviously hostile environment makes it difficult to work and make observations for long periods of time. For example, protective eye wear attenuates the light over the entire visible spectrum and thus makes it difficult to observe details which are important.
Remote viewing is desirable because it removes the human observer from the hostile environment. However, equipment shortcomings sometimes make it difficult to obtain desired results using remote viewing techniques. For example, in the system of Ariessohn et al., U.S. Pat. No. 4,539,588, a remote viewing apparatus for a smelt bed includes a video camera fitted with an infrared (IR) imaging detector or vidicon tube to detect IR emission from the smelt bed. An objective lens obtains the image and an optical filter is interposed between the lens and the vidicon tube to selectively reject radiation less than about 1 micrometer to avoid fume interference. The filter is further selected to reject all but limited ranges of radiation; for example, the filter is centered about 1.68 micrometer with a bandwidth of about 0.07 micrometer. The problem with Ariessohn et al. is that no source of illumination other than the light within the flame is available to illuminate the smelt bed, and all ambient light except the long IR radiation is filtered out.
In Justice et al., U.S. Pat. No. 4,225,771, a high intensity monochromatic light source is projected toward a welding arc and welding puddle at a selected angle. A filter tuned to the wavelength of the monochromatic light source is placed in front of a remote viewing camera at the opposite side of the arc and at the selected angle. The light enhances the welding arc background while the filter attenuates the welding arc illumination that reaches the camera in order to enhance the contrast ratio between the welding arc, the weld puddle, and the surrounding area. Justice et al. is restricted to the particular angular viewing arrangement disclosed.
In Gourog et al., U.S. Pat. No. 4,084,188, an optical scanner is disclosed for scanning an object (e.g., a document) located in space. The object is exposed to ambient light. Relatively low intensity laser light is directed at the object through a beam splitter and a scanning deflector. Light scattered from the object is reflected back through the deflector and beam splitter to an optical sensor, including, a narrow band filter, a lens, and a photo detector. The laser light is modulated at a carrier frequency rate and the electrical signal from the photo detector is demodulated to produce a video signal. Ambient light is filtered by the narrow band filter. This system uses a most complex imaging technique for document reproduction, including light modulation which is not necessary in the subject invention.
Behr, U.S. Pat. No. 4,525,462, appears to disclose a furnace sight glass that filters infrared radiation.
None of the references appear to disclose any means for discriminating between visible wavelengths present in the ambient radiation and wavelengths of external sources of illumination.
Accordingly, an improved apparatus and method for viewing the internal structures and walls of a combustion chamber is desired that will enhance details of the wall surfaces and structures, and which is adapted for direct human viewing or remote viewing, and which is relatively simple to implement.